As a typical example of a display device, a liquid crystal display device, an organic EL (Electroluminescence) device, and the like having a liquid crystal element or a light-emitting element in each pixel are represented. These display devices have a display element such as a liquid crystal element or an organic light-emitting element (hereinafter, referred to as a light-emitting element) in each of a plurality of pixels formed over a substrate. A liquid crystal element and a light-emitting element have a layer including a liquid crystal and an organic compound, respectively, between a pair of electrodes and are operated by applying a voltage or supplying a current between the pair of electrodes.
Each pixel of a display device is provided with a semiconductor element such as a transistor by which operation of a liquid crystal element and a light-emitting element is controlled. Use of such a so-called active-matrix type display device enables high-resolution display. For example, an active-matrix type organic EL display device provided with a plurality of pixels having light-emitting elements showing different colors and transistors is disclosed in Japanese patent application publication 2012-216338.